Programmable inductor

ABSTRACT

The present invention provides a programmable integrated inductor having a compact design, having a dual turn and a parallel programmable impedance. In particular, the impedance value of the programmable changes, like a variable, programmable, as its range may be set to an unlimited number of values. The invention, thus, provides a wider range of programmable values without compromising space, at a constant equivalent given inductor area.

FIELD OF THE INVENTION

The present invention relates to the field of programmable integratedinductors. In particular, the invention relates to providing a wideprogrammable inductance range within a compact area.

BACKGROUND OF THE INVENTION

Programmable inductors are essential components in Radio Frequency (RF)circuits in the domains of telecommunications, mobile communications,wireless local area networks (WLAN), TV, networking and so on. With suchdevices, many useful applications may be implemented, such asprogrammable voltage controlled oscillators (VCO), programmable filters,output buffers using a programmable over-shoot or boost, programmablefeatures, i.e., gain, linearity, matching networks, in circuits likeLNAs (Low Noise Amplifiers), mixers, power amplifiers and the like.

A traditional programmable inductor includes many inductors and switchesin order to achieve the programmability function. For example, referringto FIG. 1, a schematic diagram illustrates a conventional programmableinductor implementation using multi-inductors technique with switches.

In particular, an exemplary programmable inductor 100 is shown havingtwo conductors 102 and 104 and two switches 106 and 108. When theswitches 106 and 108 are both connected, the inductors 102 and 104 areconnected to the inductor terminals in parallel. When either of theswitches 106 and 108 have been disconnected, only inductor 102 isconnected to the inductor terminals. Therefore, with the control of theswitches 106 and 108, inductors 102 and 104 may be connected to theinductor terminals in different configurations. Consequently, twodifferent inductor values may be obtained in the inductor terminals, andthe inductance value of this inductor is programmable.

However, this type of programmable inductor presents a number oflimitations. The programmable inductor 100 takes too much area spacebecause the inductor number increases with the number of programmablevalues. Therefore, when an area of an inductor is limited, theprogrammable values range are also limited. Furthermore, because of thelarge area, an inductor's radiations and magnetic coupling with otherblocks or devices also increase, causing further performancedegradations.

For example, to address the above drawbacks, various solutions have beenadvanced. One solution presented in, namely, US Patent Application2006/0033602 A1, proposes a variable integrated inductor which has aninductance value that may be switched between two or more values. Thisreference proposes a principle based on the coupling between a primaryinductor and a secondary one, the last being programmable with switches,which makes the coupling itself variable and as a result, the value ofthe primary inductor also varies.

However, in this type of variable integrated inductor, in one scenariowhere many secondary inductor pairs are disposed in a plan with each oneplaced near one another, the inconvenience of spatial extension andincreasing coupling and radiation issues are present. In anotherscenario where these secondary inductor pairs are superposed over eachother, there is no area issue which can be invoked. Further, anotherlimitation arises resulting from the parasitic capacitors between thesecondary inductors and the substrate on a side, and the primaryinductor and the secondary inductors on the other side. These parasiticcapacitors define the own resonance frequency of the primary andsecondary inductors. The higher the capacitors are, the lower are theresonance frequencies, and an inductor may not be used at a frequencyclose or inferior to its resonance frequency. Therefore, there is alimitation on the frequency of use, resulting primarily from thesuperposition of many inductors, which may affect either the primary orthe secondary inductors. Consequently, the increase of theprogrammability range may not be implemented without giving an upwardlimitation on the utilization frequency of a given programmableinductor.

Therefore, in view of these concerns, there is a continuing need fordeveloping a new and improved programmable integrated inductor whichwould avoid the disadvantages and above mentioned problems while beingcost effective and simple to implement.

OBJECT AND SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide animproved programmable inductor as indicated according to claim 1. Inparticular, the invention includes a programmable integrated inductorincluding a dual-turn inductor with at least one inner turn and at leastone outer turn, where a current generated by the inner and the outerturn have the same direction, and at least one parallel programmableimpedance configured to change an impedance value and an inductancevalue of the inductor, where the impedance value is a variable based asa function of a digital or an analog signal and the inductance value isprogrammable so that its range may be set to an unlimited number ofvalues.

One or more of the following features may also be included.

In one aspect of the invention, the current in the inner turn isconfigured to generate a magnetic field B₁ and the current in the outerturn is configured to generate a magnetic field B₂.

In yet another aspect, the range of values of the programmable inductoris configured to increase without increasing inductor dimensions.

In another aspect, dual-turn inductor includes N number of turns, or thedual-turn inductor includes a FIG. 8 shape and further includes at leastone lower dual-turn and at least one upper dual-turn.

Embodiments may have one or more of the following advantages.

Advantageously, the present programmable integrated inductor may beimplemented in a compact area, taking no more chip area than thatrequired by traditional fixed inductors. Thus, compact design and spacesaving is achieved with an important area ratio saving. Further, thepresent invention increases the programmable inductance values range ata constant area. This new inductor area being relative to its maximumprogrammable value, the area saving results because there is no need toadd other auxiliary or supplementary inductors to get access to lowerinductor values. This permits the use of a single compact device ratherthan using many devices.

Furthermore, due mainly to the area limitation, the inductor layoutshave reduced magnetic radiations and coupling. Thus, the area savingsalso results in an improvement of magnetic coupling properties. In otherwords, the limitation of the spatial extension considerably improves thesensitivity regarding the received and emitted radiations. This avoidshigh magnetic coupling or radiations issues in circuits containingseparate and switchable inductors, which are caused mainly by thespatial extension of these conventional inductors. Thus, couplingproperties are significantly improved.

Additionally, the programmable integrated inductor provides aninductance value that can be set to any value by changing the inductancevalue of parallel impedances. With this inductance value, it is possibleto obtain either a continuous or a discrete law with the controlsignals. Further, the analog programmability option is also possiblearound any inductor value, being digitally programmable. Thus, it ispossible to have either digital or analog programmability.

Furthermore, the invention advantageously provides a novel programmableinductor with a wide range of programmable values, providing a higherprogrammability range for a given and equivalent inductor area, as wellas maximum frequency of utilization whereby the utilization of theprogrammable inductor can be carried out at much higher frequencies.

Another added value for devices implementing programmable inductors isthe ability to facilitate front-end convergence solutions, such asmaking single-block LNAs or mixers compatible with many RF bands orstandards requirements, mainly on gain and linearity parameters (IIP2,IIP3), or unifying many matching networks into a single structure thatmay be adapted to the desired RF band only by changing the inductorvalue. Any type of filters using inductors may also be easily adapted intheir characteristics by using such programmable inductors.

These and other aspects of the invention will become apparent from andelucidated with reference to the embodiments described in the followingdescription, drawings and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a traditional programmableinductor implementation using a multi-inductor assembly with switches;

FIG. 2 is a schematic diagram illustrating a fixed dual-turn inductor,illustrating the implementation of an improved method and systemaccording to one of the embodiments of the present invention;

FIG. 3 is a schematic diagram illustrating a programmable dual-turninductor, according to one of the embodiments of the present invention;

FIG. 4 is a schematic diagram illustrating a 3-turn programmableinductor, according to one of the embodiments of the present invention;

FIG. 5A is a schematic diagram illustrating a figure “8” shapeddual-turn programmable inductor, according to one of the embodiments ofthe present invention; and

FIG. 5B is a schematic diagram illustrating another derivative figure“8” shaped dual-turn programmable inductor, according to one of theembodiments of the present invention.

DESCRIPTION OF EMBODIMENTS

Referring to FIG. 2, a schematic diagram illustrates a fixed dual-turninductor 200. The inductor 200 includes an outer turn 202 and an innerturn 204. With the structure of the dual-turn inductor 200, the currentin the outer turn 202 travels in the same direction as the current inthe inner turn 204. In FIG. 2, it can be seen that both the outer turn202 and the inner turn 204 are turning clockwise, as indicated by thearrows. Consequently, the current in the outer turn 202 generates amagnetic field B₁ 206 and the current in the inner turn 204 generates amagnetic field B₂ 208.

The magnetic flux generated by each turn may be defined by the followingequation:

Φ_(k) =∫∫{right arrow over (B)} _(k) {right arrow over (d)}S (k=1,2)  [Equation No. 1]

As magnetic fields B₁ 206 and B₂ 208 have the same directions, the totalmagnetic flux inside the dual-turn inductor 200 is the addition of themagnetic flux Φ₁ and Φ₂, where Φ₁ is the magnetic flux calculated fromthe magnetic field B₁ 206 by Equation No. 1 and Φ₂ is the magnetic fluxcalculated from the magnetic field B₂ 208. The inductance value of thefixed dual-turn inductor 200 may be defined as follows:

L=Φ _(tot) /i=(Φ₁+Φ₂+ . . . +Φ_(k))/i  [Equation No. 2]

Referring now to FIG. 3, a schematic diagram illustrates a programmabledual-turn inductor 300, which includes a dual-turn inductor outer turn302 and an inner turn 304 with a parallel programmable impedance 310.The structure of the dual-turn inductor 300 is the same as the fixeddual-turn inductor 200.

If the current in the outer turn 302 has the same value and direction asthe current in the outer turn 202 as shown in FIG. 2, the current in theinner turn 304 is lower than the current in the inner turn 204 of thefixed dual-turn inductor 200 of FIG. 2. The current i is separated intotwo branches at point 312 where one branch i′ crosses over to the innerturn 304 and another Δi proceeds to go through the impedance 310. Thesetwo branches then combine at point 314. The current i′ is given byfollowing equation:

i′=i−Δi  [Equation No. 3]

The current i′ in the inner turn 304 is lower than the current i in theinner turn 204 of FIG. 2. A generated magnetic field 308 of the innerturn 304 is lower than the generated magnetic field 208. As indicated bythe Equation No. 1, the magnetic flux generated by the inner turn 204 islower. Referring then to Equation No. 2, since the value of current i isfixed, the inductance value of the inductor 300 will be lower than thatof the inductor 200.

By making the impedance value of the impedance 310 vary as a function ofa digital or an analog signal, the inner current i′ may be modulated.When the impedance value of 310 is changed, Δi is changed, then i′ issimilarly modified based on Equation No. 3. According to Equations No. 1and No. 2, the current i′, the magnetic field, the total flux, and theinductance value may be modulated. In this way, regardless of a discreteor a continuous law, the inductance value can be realized as a functionof the control signal. The analog programmability option is possiblearound any inductor value, being digitally programmable. And theinductance value may be set to as many values as desired in theavailable range.

The variable impedance may be realized with a programmabletrans-conductance or impedance, e.g., a MOS device, with a voltagesignal controlling the gate. The variable impedance may also be realizedby using a small Varicap (diode) block in parallel, providing an ACparallel path as a function of a tune voltage signal, i.e., using smallsize Varicaps to ensure a very high resonance frequency.

The added parasitics by the MOS switches are much lower and negligibleif compared to those created by the secondary inductors, this being trueregardless of whether the secondary inductor is single or multiple. Thesecondary inductor, i.e., single or multiple, being built with widemetal layers, generates naturally higher parasitic capacitors than theMOS switches. Therefore, for a given and equivalent programmabilityrange, the utilization of the programmable inductor may be performed atmuch higher frequencies.

The possible degradation of the quality Q-factor may be considered to bean inconvenience due to the parallel impedance influence. However, thedegradation may be roughly comparable to implementations that use simpleswitches. Many applications do not require high levels of Q-factor, suchas broadband applications or blocks where linearity or gain/boostprogrammability specifications are more critical than noise orselectivity aspects.

In order to achieve a wider range of programmable values at a constantarea, a dual-turn programmable inductor may be extended to an N-turnsprogrammable inductor. For example, referring to FIG. 4, a 3-turnprogrammable inductor 400 is shown. The conductor has the form of a3-turn inductor as shown by turns 402, 404 and 406 and two parallelprogrammable impedances 408 and 410. This particular configurationoffers the additional third turn 406 and the additional parallelprogrammable impedance 410 to the dual-turn inductor 300, illustrated inFIG. 3. As shown, arrows indicate the direction of the currents in thisexemplary 3-turn programmable inductor 400.

For example, if the current in the first turn 402 is i, the current i′in the second turn 404 may be given by the Equation No. 3. The currenti″ in the third turn 406 may be given by the following relation:

i″=i′−Δi′=i−Δi−Δi′  [Equation No. 4]

The impedance values of the parallel programmable impedance 408 and 410may be modulated by two separated signals, and then current Δi and Δi′are under control. Referring to the foregoing Equations Nos. 1-4, theinductance value of the inductor 400 is a variable one. By making theimpedance value of the programmable impedances 408 and 410 a function ofa digital or an analog signal, the inductance value of the inductor 400is programmable and may be set to as many values as desired in theavailable range.

Although in FIG. 4, a 3-turn programmable inductor has been shown anddescribed, it may also be possible to implement more than a 3-turnprogrammable inductor which enables a much wider inductance value range.

Referring now to FIG. 5A, a schematic diagram illustrates afigure-8-shaped dual-turn programmable inductor 500, which presents thefeatures of the previous configurations and further reduced couplingproperties. The inductor 500 has the form of a dual-turn figure “8”shaped structure or configuration with two lower dual-turns 502 and 504,upper dual-turns 506 and 508 and two programmable impedances 510 and512.

By virtue of the figure “8” shape, currents in the upper dual-turns 506and 508 travel in a direction, e.g., counterclockwise, that is oppositeto the current direction in the lower dual-turns 502 and 504, whichhappens to be clockwise. Consequently, the figure “8” shape geometry hasthe advantage that the magnetic fields which emanate from the lowerdual-turns 502 and 504 and the upper dual-turns 506 and 508 haveopposing directions. As a result, the coupling properties are reduced.

Still referring to FIG. 5A, if the current in the lower dual-turn 502 isi, the current i′ in the upper dual-turns 506 and 508 may be given bythe Equation No. 3, and the current i″ in the lower dual-turn 504 may begiven by the Equation No. 4. With respect to Equations Nos. 1 and 2, theinductance value of the inductor 500 is variable by modulating theimpedance values of the programmable impedances 510 and 512. By makingthe impedance value of the programmable impedances 510 and 512 afunction of a digital or an analog signal, the inductance value of theinductor 500 is programmable and can be set to as many values as desiredin the available range.

Referring now to FIG. 5B, a schematic diagram illustrates anotherderivative figure “8” shaped dual-turns programmable inductor 500B,which allows more symmetrical current distributions and magnetic fields.The inductor 500B is a derivative inductor from inductor 500 of FIG. 5A.Analogously, inductor 500B has the lower dual-turns 502B and 504B, andupper dual-turns 506B and 508B structure. However, inductor 500B has anvariable impedance 512B positioned at the top of the inductor 500B.

By virtue of the figure “8” shape, current in the upper dual-turnstravels in a direction opposite to the current in the lower dual-turns.If the current in the lower dual-turn 502B is i, the current in upperturn 508B is still i and the current in the lower turn 504B and upperturn 506B may be i′, which can given by the Equation No. 3. With respectto Equations Nos. 1 and 2, the inductance value of the inductor 500B isa variable by modulating the impedance values of the programmableimpedances 512B.

Referring back to inductor 500A of FIG. 5, which has i′+i′ and i+i″total currents, respectively, for the upper and lower turns, the valuesof i′+i′ and i+i″ are not identical at all times. With respect toEquation No. 1, the upper and the lower magnetic fields may not besymmetrical, depending on the programmable impedances values.Comparatively, the inductor 500B has i′+i and i+i′ total currents,respectively, for the upper and the lower turns. Total currents i′+i andi+i′ always have the same value. This results in more symmetrical upperand lower magnetic fields, regardless of the programmable impedancevalue.

Therefore, inductor 500B in FIG. 5B allows more symmetrical currentsdistributions and magnetic fields between the upper-turns and thelower-turns. Consequently, this improves the external magnetic andcoupling suppression properties for the inductor 500B configuration.

Although the figure “8” shape dual-turn programmable inductor has beenshown and described above with reference to FIG. 5B, it is also possibleto implement a derivative figure “8” shaped N-turn programmable inductorwhich enables a wider inductance value range.

An implementation of a programmable dual-turn inductor using an NMOStransistor as a parallel impedance has been carried out over atest-chip. For example, the NMOS size may be W=150 μm, L=0.25 μm,stripes=5. In this example, the programmable dual-turn inductor includesa dual-turn inductor and a NMOS used as a parallel impedance and aninductor control pad. The impedance control is made with a voltagepotential applied directly on the gate.

While there has been illustrated and described what are presentlyconsidered to be the preferred embodiments of the present invention, itwill be understood by those of ordinary skill in the art that variousother modifications may be made, and equivalents may be substituted,without departing from the true scope of the present invention.

Additionally, many advanced modifications may be made to adapt aparticular situation to the teachings of the present invention withoutdeparting from the central inventive concept described herein.Furthermore, an embodiment of the present invention may not include allof the features described above. Therefore, it is intended that thepresent invention not be limited to the particular embodimentsdisclosed, but that the invention include all embodiments falling withinthe scope of the appended claims and their equivalents.

1. A programmable integrated inductor comprising: a dual-turn inductorcomprising at least one inner turn and at least one outer turn, whereina current generated by the at least one inner and a current generated bythe at least one outer turn have a same direction; and at least oneparallel programmable impedance configured to change an impedance valueand an inductance value of the inductor, wherein the impedance value isa variable based as a function of a digital or an analog signal and theinductance value is programmable so that its range may be set to anunlimited number of values.
 2. The programmable inductor of claim 1,wherein the current in the at least one inner turn is configured togenerate a magnetic field B1 and the current in the at least one outerturn is configured to generate a magnetic field B2.
 3. The programmableinductor of claim 2, wherein a magnetic flux generated by the respectivecurrents of the inner and the outer turns is defined by, wherein kequals 1 for the at least one inner turn and k equals 2 for the at leastone outer turn and Ö1 indicates the magnetic field of the inner turn andÖ2 indicates the magnetic field of the outer turn.
 4. The programmableinductor of claim 3, wherein the inductance value of the dual-turninductor is defined by wherein is the total magnetic flux generated bythe respective inner and outer turns.
 5. The programmable inductor ofclaim 1, wherein the range of values of the programmable inductor isconfigured to increase without increasing inductor dimensions.
 6. Theprogrammable inductor of claim 1, wherein the variable impedance may beimplemented using a programmable trans-conductance or impedance device.7. The programmable inductor of claim 1, wherein the variable impedancemay be implemented using a Varicap block in parallel, providing an ACparallel path as a function of a tune voltage signal.
 8. Theprogrammable inductor of claim 1, wherein the dual-turn inductorcomprises N number of turns.
 9. The programmable inductor of claim 1,wherein the dual-turn inductor comprises a “figure eight” shape andfurther comprises at least one lower dual-turn and at least one upperdual-turn.
 10. The programmable inductor of claim 1 further comprising aNMOS transistor configured as the parallel impedance and an inductorcontrol pad, wherein its impedance control is made with a voltagepotential applied directly on a gate.
 11. A method of manufacturing aprogrammable integrated inductor, comprising: forming a dual-turninductor comprising at least one inner turn and at least one outer turn,wherein a current generated by the at least one inner and a currentgenerated by the at least one outer turn have a same direction; andforming at least one parallel programmable impedance configured tochange an impedance value and an inductance value of the inductor, andwherein the impedance value is a variable based as a function of adigital or an analog signal and the inductance value is programmable sothat its range may be set to an unlimited number of values.
 12. Themethod of claim 11, wherein the current in the at least one inner turngenerates a magnetic field B1 and the current in the at least one outergenerates a magnetic field B2.
 13. The method of claim 12, wherein amagnetic flux generated by the respective currents of the inner and theouter turns is defined by, wherein k equals 1 for the at least one innerturn and k equals 2 for the at least one outer turn and Ö1 indicates themagnetic field of the inner turn and Ö2 indicates the magnetic field ofthe outer turn.
 14. The method of claim 13, wherein the inductance valueof the dual-turn inductor is defined by wherein is the total magneticflux generated by the respective inner and outer turns.
 15. The methodof claim 11, further comprising using a programmable trans-conductanceor impedance device to implement the variable impedance.
 16. The methodof claim 11, wherein the dual-turn inductor comprises N number of turns.17. The method of claim 11, wherein the dual-turn inductor comprises a“figure eight” shape and further comprises at least one lower dual-turnand at least one upper dual-turn.
 18. A wireless communication devicecomprising a programmable integrated inductor comprising: a dual-turninductor comprising at least one inner turn and at least one outer turn,wherein a current generated by the at least one inner and a currentgenerated by the at least one outer turn have a same direction; and atleast one parallel programmable impedance configured to change animpedance value and an inductance value of the inductor, wherein theimpedance value is a variable based as a function of a digital or ananalog signal and the inductance value is programmable so that its rangemay be set to an unlimited number of values.
 19. The programmableinductor of claim 18, wherein the range of values of the programmableinductor is configured to increase without increasing inductordimensions.
 20. The programmable inductor of claim 18, wherein thevariable impedance may be implemented using a programmabletrans-conductance or impedance device.